1. Field of the Invention
The present invention relates to interchangeable injection molding dies for plastics injection molding machines and, more particularly, to a latching device which operates to automatically lock together of the two halves of an injection molding die, when they are not attached to the die carrier members of the die closing unit of the injection molding machine.
2. Description of the Prior Art
Prior to the recent development of injection molding machines with automated die changing mechanisms, it has not been necessary or desirable to equip the interchangeable injection molding dies with special latching means, in order to prevent the separation of the two die halves of a die assembly during handling and manipulation of the latter, before and after the two die halves are attached to the stationary and movable die carrier members of the die closing unit of the machine.
As a rule, such handling and manipulation involved the use of a hoist engaging hoisting eyes on both die halves, so that adequate safety was provided against an accidental separation of the die halves.
However, the automation of the die changing procedure, involving the mechanized removal of the previously used die assembly and the simultaneous insertion and automatic attachment of another die assembly--including, as the case may be, the automatic uncoupling and coupling of various electrical and fluid carrying lines connecting the die assembly to the injection molding machine--had made it necessary to positively prevent a separation, even a small partial separation, of the two die halves during the die changing procedure.
A previously suggested solution to this requirement involves the arrangement of a latching bar or fishplate on one side of the die assembly by means of which the two die halves are latched together (European Patent Application No. 0 092 686 Al, published Nov. 2, 1983).
This latching arrangement has the shortcoming of necessitating a special manual operation for the placement and removal of the fishplate, which operation can readily be omitted, either accidentally or intentionally. Accordingly, it does not qualify as an adequate passive safety device against the separation of the die halves during the mechanized die exchange procedure. The additional disadvantage of the fishplate needing to be removed from the die assembly and stowed away during operation of the machine represents a temptation for machine operators not to use it.